DNS Extensions Working Group                                     S. Rose
Internet-Draft                                                      NIST
Intended status: Standards Track                           W. Wijngaards
Expires: February 11, March 28, 2008                                       NLnet Labs
                                                         August 10,
                                                      September 25, 2007

                 Update to DNAME Redirection in the DNS
                 draft-ietf-dnsext-rfc2672bis-dname-04
                 draft-ietf-dnsext-rfc2672bis-dname-05

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   The DNAME record provides redirection for a sub-tree of the domain
   name tree in the DNS system.  That is, all names that end with a
   particular suffix are redirected to another part of the DNS.  This is
   an update to the original specification in RFC 2672.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

   2.  The DNAME Resource Record  . . . . . . . . . . . . . . . . . .  3
     2.1.  Format . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.2.  The DNAME Substitution . . . . . . . . . . . . . . . . . .  4
     2.3.  DNAME Apex not Redirected itself . . . . . . . . . . . . .  5
     2.4.  Names Next to and Below a DNAME Record . . . . . . . . . .  5
     2.5.  Compression of the DNAME record. . . . . . . . . . . . . .  6

   3.  Processing . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  Wildcards  . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  CNAME synthesis  . . . . . . . . . . . . . . . . . . . . .  6
     3.3.  Acceptance and Intermediate Storage  . . . . . . . . . . .  7
     3.4.  Server algorithm . . . . . . . . . . . . . . . . . . . . .  7

   4.  DNAME Discussions in Other Documents . . . . . . . . . . . . .  9

   5.  Other Issues with DNAME  . . . . . . . . . . . . . . . . . . . 11
     5.1.  MX, NS and PTR Records Must Point to Target of DNAME . . . 11
     5.2.  Dynamic Update and DNAME . . . . . . . . . . . . . . . . . 11
     5.3.  DNSSEC and DNAME . . . . . . . . . . . . . . . . . . . . . 11
       5.3.1.  DNAME bit in NSEC/NSEC3 type map . . . . . . . . . . . 11
       5.3.2.  Other issues with NSEC3 and DNAME  . . . . . . . . . . 12
       5.3.3.  Validators Must Understand DNAME . . . . . . . . . . . 12
         5.3.3.1.  DNAME in Bitmap Causes Invalid Name Error  . . . . 12
         5.3.3.2.  Valid Name Error Response Involving DNAME in
                   Bitmap . . . . . . . . . . . . . . . . . . . . . . 12
         5.3.3.3.  Response With Synthesized CNAME  . . . . . . . . . 13

   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13

   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13

   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 14

   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 15

1.  Introduction

   DNAME is a DNS Resource Record type.  DNAME provides redirection from
   a part of the DNS name tree to another part of the DNS name tree.

   For example, given a query for foo.example.com and a DNAME from
   example.com to example.net, the query would be redirected to
   foo.example.net.  With the same DNAME a query for foo.bar.example.com
   would be redirected to foo.bar.example.net.

   The DNAME RR is similar to the CNAME RR in that it provides
   redirection.  The CNAME RR only provides redirection for exactly one
   name while the DNAME RR provides redirection for all names in a sub-
   tree of the DNS name tree.

   This document is an update to the original specification of DNAME in
   RFC 2672 [RFC2672].  DNAME was conceived to help with the problem of
   maintaining address-to-name mappings in a context of network
   renumbering.  So that with  With a careful set-up set-up, a renumbering event in the
   network causes no change to the authoritative server that has the
   address-to-name mappings.  Examples in practice are classless reverse
   address space delegations and punycode alternates for domain spaces.

   Other usage of DNAME lies in redirection of name spaces.  For
   example, a zone administrator may want subtrees of the DNS to contain
   the same information.  DNAME is also used for redirection of ENUM
   domains to another maintaining party.

   This update to DNAME does not change the wire format or the handling
   of DNAME Resource Records by existing software.  A new UD (Understand
   Dname)
   DNAME) bit in the EDNS flags field can be used to signal that CNAME
   synthesis is not needed.  Discussion is added on problems that may be
   encountered when using DNAME.

2.  The DNAME Resource Record

2.1.  Format

   The DNAME RR has mnemonic DNAME and type code 39 (decimal).

   The format of the DNAME record has not changed from the original
   specification in RFC 2672.  DNAME has the following format:

           <owner> <ttl> <class> DNAME <target>

   The format is not class-sensitive.  All fields are required.  The
   RDATA field target is a domain name.  The RDATA field target name
   MUST be sent uncompressed [RFC3597].

   The DNAME RR causes type NS additional section processing.

2.2.  The DNAME Substitution

   DNAMEs cause a name substitution to happen to query names.  This is
   called the DNAME substitution.  The suffix owner name of the DNAME is
   replaced by the target of the DNAME.  The owner name of the DNAME is
   not itself redirected, only domain names below the owner name are
   redirected.  Only whole labels are replaced.  A name is considered
   below the owner name if it has more labels than the owner name, and
   the labels of the owner name appear as the suffix of the name.  See
   the table of examples for common cases and corner cases.

   In the table below, the QNAME refers to the query name.  The owner is
   the DNAME owner domain name, and the target refers to the target of
   the DNAME record.  The result is the resulting name after performing
   the DNAME substitution on the query name. "no match" means that the
   query did not match the DNAME and thus no substitution is performed
   and a possible error message is returned (if no other result is
   possible).  In the examples below, 'cyc' and 'shortloop' contain
   loops.

    QNAME            owner  DNAME   target         result
    ---------------- -------------- -------------- -----------------
    com.             example.com.   example.net.   <no match>
    example.com.     example.com.   example.net.   <no match>
    a.example.com.   example.com.   example.net.   a.example.net.
    a.b.example.com. example.com.   example.net.   a.b.example.net.
    ab.example.com.  b.example.com. example.net.   <no match>
    foo.example.com. example.com.   example.net.   foo.example.net.
    a.x.example.com. x.example.com. example.net.   a.example.net.
    a.example.com.   example.com.   y.example.net. a.y.example.net.
    cyc.example.com. example.com.   example.com.   cyc.example.com.
    cyc.example.com. example.com.   c.example.com. cyc.c.example.com.
    shortloop.x.x.   x.             .              shortloop.x.
    shortloop.x.     x.             .              shortloop.

                   Table 1. DNAME Substitution Examples.

   It is possible for DNAMEs to form loops.  Just like CNAMEs can form
   loops.  DNAMEs and CNAMEs can chain together to form loops.  A single
   corner case DNAME can form a loop.  Resolvers and servers should be
   cautious in devoting resources to a query, but be aware that fairly
   long chains of DNAMEs may be valid.  Zone content administrators
   should take care to insure that there are no loops that could occur
   when using DNAME or DNAME/CNAME redirection.

   The domain name can get too long during substitution.  For example,
   suppose the target name of the DNAME RR is 250 octets in length
   (multiple labels), if an incoming QNAME that has a first label over 5
   octets in length, the result of the result would be a name over 255
   octets.  If this occurs the server returns an RCODE of YXDOMAIN
   [RFC2136].  The DNAME record and its signature (if the zone is
   signed) are included in the answer as proof for the YXDOMAIN (value
   6) RCODE.

2.3.  DNAME Apex not Redirected itself

   The owner name of a DNAME is not redirected itself.  The reason for
   the original decision was that one can have a DNAME at the zone apex
   without problem.  Then use this DNAME at the zone apex to point
   queries to the target zone.  There still is a need to have the
   customary SOA and NS resource records at the zone apex.  This means
   that DNAME does not mirror a zone completely, as it does not mirror
   the zone apex.

   Another reason for excluding the DNAME owner from the DNAME
   substitution is that one can then query for the DNAME through RFC
   1034 [RFC1034] caches.

   This means that a DNAME RR is not allowed at the same domain name as
   NS records unless there is also a SOA record present.  DNAME RRs are
   not allowed at the parent side of a delegation point but are allowed
   at a zone apex.

2.4.  Names Next to and Below a DNAME Record

   Other resource records MUST NOT exist below the owner of a DNAME RR.
   To get the contents for names subordinate to that owner, the DNAME
   redirection must be invoked and the resulting target queried.  A
   server SHOULD refuse to load a zone that has data below a domain name
   owning a DNAME RR.  Also a server SHOULD refuse to load a zone
   subordinate to the owner of a DNAME record in the ancestor zone.

   DNAME is a singleton type, meaning only one DNAME is allowed per
   name.  The owner name of a DNAME can only have one DNAME RR, and no
   CNAME RRs can exist at that name.  These rules make sure that for a
   single domain name only one redirection exists, and thus no confusion
   which one to follow.  A server SHOULD refuse to load a zone that
   violates these rules.

   The domain name that owns a DNAME record is allowed to have other
   resource record types at that domain name, except DNAMEs or CNAMEs.

   These rules allow DNAME records to be queried through DNAME unaware
   caches.

2.5.  Compression of the DNAME record.

   The DNAME owner name can be compressed like any other owner name.
   The DNAME RDATA target name MUST NOT be sent out in compressed form,
   so that a DNAME RR can be treated as an unknown type.

   Although the previous specification [RFC2672] talked about signaling
   to allow compression of the target name, no such signaling is
   explicitly specified.

   RFC2672 stated that the EDNS version had a meaning for understanding
   of DNAME and DNAME target name compression.  This document updates
   RFC2672, in that there is no EDNS version signaling for DNAME as of
   yet.  However, the flags section of EDNS(0) is updated with a
   Understand-DNAME flag by this document (See Section 3.2).

3.  Processing

3.1.  Wildcards

   The use of DNAME in conjunction with wildcards is discouraged
   [RFC4592].  Thus records of the form "*.example.com DNAME
   example.net" SHOULD NOT be used.

   The interaction between the expansion of the wildcard and the
   redirection of the DNAME is non-deterministic.  Because the
   processing is non-deterministic, DNSSEC validating resolvers may not
   be able to validate a wildcarded DNAME.

   A server MAY give a warning that the behavior is unspecified if such
   a wildcarded DNAME is loaded.

3.2.  CNAME synthesis

   On the server side, the DNAME RR record is always included in the
   answer section of a query.  A CNAME RR record with TTL 0 is
   synthesized for old resolvers, specifically for the QNAME in the
   query.  DNSSEC [RFC4033], [RFC4034], [RFC4035] says that the
   synthesized CNAME does not have to be signed.  The DNAME has an RRSIG
   and a validating resolver can check the CNAME against the DNAME
   record and validate the DNAME record.

   It does not make sense for the authoritative server to follow the
   chain of DNAMEs, CNAMEs and wildcards outside of the zone of the
   query, as modern resolvers will remove out-of-zone information from
   the answer.

   Resolvers MUST be able to handle a synthesized CNAME TTL of zero or
   equal to the TTL of the corresponding DNAME record.  The TTL of zero
   means that the CNAME can be discarded immediately after processing
   the answer.  DNSSEC  DNAME aware resolvers can set the Understand-DNAME (UD
   bit) to receive a response with only the DNAME RR and no synthesized
   CNAMEs.

   The UD bit is part of the EDNS extended RCODE and Flags field.  It is
   used to omit server processing, transmission and resolver processing
   the
   of unsigned synthesized CNAMEs when DNSSEC validation is performed. CNAMEs.  Resolvers can set this in a query to
   request omission of the synthesized CNAMEs.  Servers copy the UD bit
   to the response, and can omit synthesized CNAMEs from the answer.
   Older resolvers do not set the UD bit, and older servers do not copy
   the UD bit to the answer, and will not omit synthesized CNAMEs.

   Updated EDNS extended RCODE and Flags field.

               +0 (MSB)                +1 (LSB)
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
   0: |   EXTENDED-RCODE      |       VERSION         |
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
   2: |DO|UD|                 Z                       |
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

   Servers MUST be able to answer a query for a synthesized CNAME.  An
   answer containing the synthesized CNAME cannot contain an error
   (since a CNAME has been followed), as per RFC 1034 CNAME rules.

3.3.  Acceptance and Intermediate Storage

   DNS Caches MUST NOT allow data to be cached below the owner of a
   DNAME RR, except CNAME records or perhaps NSEC3 records and their
   signatures.  CNAME records below the owner of a DNAME MUST be re-
   synthesized from the DNAME, or checked against the DNAME record
   before sending them out.  This improves consistency of the DNAME and
   CNAME records below the owner of the DNAME.

   DNS Caches MUST perform CNAME synthesis on behalf of DNAME-ignorant
   clients.  A DNS Cache that understands DNAMEs can send out queries on
   behalf of clients with the UD bit set.  After receiving the answers
   the DNS Cache sends replies to DNAME ignorant clients that include
   DNAMEs and synthesized CNAMEs.

3.4.  Server algorithm

   Below the server algorithm, which appeared in RFC 2672 Section 4.1,
   is expanded to handle the UD bit.

   1.  Set or clear the value of recursion available in the response
       depending on whether the name server is willing to provide
       recursive service.  If recursive service is available and
       requested via the RD bit in the query, go to step 5, otherwise
       step 2.

   2.  Search the available zones for the zone which is the nearest
       ancestor to QNAME.  If such a zone is found, go to step 3,
       otherwise step 4.

   3.  Start matching down, label by label, in the zone.  The matching
       process can terminate several ways:

       A.  If the whole of QNAME is matched, we have found the node.

           If the data at the node is a CNAME, and QTYPE does not match
           CNAME, copy the CNAME RR into the answer section of the
           response, change QNAME to the canonical name in the CNAME RR,
           and go back to step 1.

           Otherwise, copy all RRs which match QTYPE into the answer
           section and go to step 6.

       B.  If a match would take us out of the authoritative data, we
           have a referral.  This happens when we encounter a node with
           NS RRs marking cuts along the bottom of a zone.

           Copy the NS RRs for the subzone into the authority section of
           the reply.  Put whatever addresses are available into the
           additional section, using glue RRs if the addresses are not
           available from authoritative data or the cache.  Go to step
           4.

       C.  If at some label, a match is impossible (i.e., the
           corresponding label does not exist), look to see whether the
           last label matched has a DNAME record.

           If a DNAME record exists at that point, copy that record into
           the answer section.  If substitution of its <target> for its
           <owner> in QNAME would overflow the legal size for a <domain-
           name>, set RCODE to YXDOMAIN [RFC2136] and exit; otherwise
           perform the substitution and continue.  If the EDNS OPT
           record is present in the query and the UD bit is set, the
           server MAY copy the UD bit to the answer EDNS OPT record, and
           omit CNAME synthesis.  Else the server MUST synthesize a
           CNAME record as described above and include it in the answer
           section.  Go back to step 1.

           If there was no DNAME record, look to see if the "*" label
           exists.

           If the "*" label does not exist, check whether the name we
           are looking for is the original QNAME in the query or a name
           we have followed due to a CNAME or DNAME.  If the name is
           original, set an authoritative name error in the response and
           exit.  Otherwise just exit.

           If the "*" label does exist, match RRs at that node against
           QTYPE.  If any match, copy them into the answer section, but
           set the owner of the RR to be QNAME, and not the node with
           the "*" label.  If the data at the node with the "*" label is
           a CNAME, and QTYPE doesn't match CNAME, copy the CNAME RR
           into the answer section of the response changing the owner
           name to the QNAME, change QNAME to the canonical name in the
           CNAME RR, and go back to step 1.  Otherwise, Go to step 6.

   4.  Start matching down in the cache.  If QNAME is found in the
       cache, copy all RRs attached to it that match QTYPE into the
       answer section.  If QNAME is not found in the cache but a DNAME
       record is present at an ancestor of QNAME, copy that DNAME record
       into the answer section.  If there was no delegation from
       authoritative data, look for the best one from the cache, and put
       it in the authority section.  Go to step 6.

   5.  Use the local resolver or a copy of its algorithm to answer the
       query.  Store the results, including any intermediate CNAMEs and
       DNAMEs, in the answer section of the response.

   6.  Using local data only, attempt to add other RRs which may be
       useful to the additional section of the query.  Exit.

   Note that there will be at most one ancestor with a DNAME as
   described in step 4 unless some zone's data is in violation of the
   no-descendants limitation in section 3.  An implementation might take
   advantage of this limitation by stopping the search of step 3c or
   step 4 when a DNAME record is encountered.

4.  DNAME Discussions in Other Documents

   In [RFC2181], in Section 10.3., the discussion on MX and NS records
   touches on redirection by CNAMEs, but this also holds for DNAMEs.

   Excerpt from 10.3.  MX and NS records (in RFC 2181).

           The domain name used as the value of a NS resource record,
           or part of the value of a MX resource record must not be
           an alias.  Not only is the specification clear on this
           point, but using an alias in either of these positions
           neither works as well as might be hoped, nor well fulfills
           the ambition that may have led to this approach.  This
           domain name must have as its value one or more address
           records.  Currently those will be A records, however in
           the future other record types giving addressing
           information may be acceptable.  It can also have other
           RRs, but never a CNAME RR.

   The DNAME RR is discussed in RFC 3363, section 4, on A6 and DNAME.
   [RFC3363] does NOT RECOMMENDED the use of DNAME in the IPv6 reverse
   tree.  (Hence, all references to DNAME should have been removed from
   [RFC4294].)  Based on the experience gained in the meantime, RFC 3363
   should be revised, dropping all constraints on having DNAME RRs in
   these zones.  This would greatly improve the manageability of the
   IPv6 reverse tree.  These changes are made explicit below.

   In [RFC3363], section 4, DNAME is not recommended for the IPv6
   reverse tree.  The opening premise of this section is demonstrably
   wrong.  Everything that follows from that premise is also invalid.

   In [RFC3363], the paragraph

     "The issues for DNAME in the reverse mapping tree appears to be
     closely tied to the need to use fragmented A6 in the main tree: if
     one is necessary, so is the other, and if one isn't necessary, the
     other isn't either.  Therefore, in moving RFC 2874 to experimental,
     the intent of this document is that use of DNAME RRs in the reverse
     tree be deprecated."

   is to be replaced with the word "DELETED".

   In [RFC4294], the reference to DNAME was left in as a editorial
   oversight.  The paragraph

     "Those nodes are NOT RECOMMENDED to support the experimental A6 and
     DNAME Resource Records [RFC3363]."
   is to be replaced by

     "Those nodes are NOT RECOMMENDED to support the experimental
     A6 Resource Record [RFC3363]."

5.  Other Issues with DNAME

   There are several issues to be aware of about the use of DNAME.

5.1.  MX, NS and PTR Records Must Point to Target of DNAME

   The names listed as target names of MX, NS and PTR records must be
   canonical hostnames.  This means no CNAME or DNAME redirection may be
   present during DNS lookup of the address records for the host.  This
   is discussed in RFC 2181 [RFC2181], section 10.3, and RFC 1912
   [RFC1912], section 2.4.

   The upshot of this is that although the lookup of a PTR record can
   involve DNAMEs, the name listed in the PTR record can not fall under
   a DNAME.  The same holds for NS and MX records.  For example, when
   punycode alternates for a zone use DNAME then the NS, MX and PTR
   records that point to that zone must use names without punycode in
   their RDATA.  What must be done then is to have the domain names with
   DNAME substitution already applied to it as the MX, NS, PTR data.
   These are valid canonical hostnames.

5.2.  Dynamic Update and DNAME

   Zones containing a DNAME RR MUST NOT accept a dynamic update message
   that would add a record or delegation with a name existing under a
   DNAME.

   A server MUST return an error message with RCODE=REFUSED [RFC2136] in
   response to a dynamic update message that would add a resource record
   under a DNAME in the zone.

5.3.  DNSSEC and DNAME

5.3.1.  DNAME bit in NSEC/NSEC3 type map

   When a validator checks the NSEC/NSEC3 RRs returned on a name error
   response, it SHOULD check that the DNAME bit is not set.  If the
   DNAME bit is set then the DNAME substitution should have been done,
   but has not.

5.3.2.  Other issues with NSEC3 and DNAME

   NSEC3 records and their signatures are allowed to exist below the
   owner name of a DNAME RR.  This is because of the nature of NSEC3 RRs
   in DNSSEC, which creates hashed owner names that exist below the apex
   name of the zone.  This is an exception to the rule that there MUST
   NOT be any other RRs under the owner name of a DNAME RR, if the DNAME
   RR is owned by the zone apex domain name.

   Queries for NSEC3 owner names are redirected as if there were no such
   NSEC3 present.

   There is no significant extra hashing cost for NSEC3 signed zones
   when answering queries with DNAME substitution.

5.3.3.  Validators Must Understand DNAME

   Examples of why DNSSEC validators MUST understand DNAME.

5.3.3.1.  DNAME in Bitmap Causes Invalid Name Error

   ;; Header: QR AA DO RCODE=3(NXDOMAIN)
   ;; Question
   foo.bar.example.com. IN A
   ;; Answer
   bar.example.com. NSEC dub.example.com. A DNAME
   bar.example.com. RRSIG NSEC [valid signature]

   If this is the response, then only by understanding that the DNAME
   bit means that foo.bar.example.com needed to have been redirected by
   the DNAME, the validator can see that it is a BOGUS reply from an
   attacker that collated existing records from the DNS to create a
   confusing reply.

   If the DNAME bit had not been set in the NSEC record above then the
   answer would have validated as a correct name error response.

5.3.3.2.  Valid Name Error Response Involving DNAME in Bitmap
   ;; Header: QR AA DO RCODE=3(NXDOMAIN)
   ;; Question
   cee.example.com. IN A
   ;; Answer
   bar.example.com. NSEC dub.example.com. A DNAME
   bar.example.com. RRSIG NSEC [valid signature]

   If the query had been cee.example.com as shown above, then this
   answer would have been validated, because 'cee' does not get
   redirected by the DNAME at 'bar'.

5.3.3.3.  Response With Synthesized CNAME

   ;; Header: QR AA DO RCODE=0(NOERROR)
   ;; Question
   foo.bar.example.com. IN A
   ;; Answer
   bar.example.com. DNAME bar.example.net.
   bar.example.com. RRSIG DNAME [valid signature]
   foo.bar.example.com. CNAME foo.bar.example.net.

   The answer shown above has the synthesized CNAME included.  However,
   the CNAME has no signature, since the server does not sign online (it
   is a slow operation and exposes the signing key).  So it cannot be
   trusted.  It could be altered by an attacker to be
   foo.bar.example.com CNAME bla.bla.example.  The DNAME record does
   have its signature included, since it does not change for every query
   name.  The validator must verify the DNAME signature and then
   recursively resolve further to query for the foo.bar.example.net A
   record.

6.  IANA Considerations

   The main purpose of this draft is to discuss issues related to the
   use of DNAME RRs in a DNS zone.  The original document registered the
   DNAME Resource Record type code 39 (decimal).  IANA should update the
   DNS resource record registry by adding a pointer to this document for
   RR type 39.

   This draft requests the second highest bit in the EDNS flags field
   for the Understand-DNAME (UD) flag.

7.  Security Considerations

   DNAME redirects queries elsewhere, which may impact security based on
   policy and the security status of the zone with the DNAME and the
   redirection zone's security status.

   If a validating resolver accepts wildcarded DNAMEs, this creates
   security issues.  Since the processing of a wildcarded DNAME is non-
   deterministic and the CNAME that was substituted by the server has no
   signature, the resolver may choose a different result than what the
   server meant, and consequently end up at the wrong destination.  Use
   of wildcarded DNAMEs is discouraged in any case [RFC4592].

   A validating resolver MUST understand DNAME, according to [RFC4034].
   In Section 5.3.3 examples are given that illustrate this need.  These
   examples are shown with NSEC records, but similar cases exist for
   NSEC3.

8.  Acknowledgments

   The authors of this draft would like to acknowledge Matt Larson for
   beginning this effort to address the issues related to the DNAME RR
   type.

9.  References

9.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2136]  Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
              "Dynamic Updates in the Domain Name System (DNS UPDATE)",
              RFC 2136, April 1997.

   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, July 1997.

   [RFC2672]  Crawford, M., "Non-Terminal DNS Name Redirection",
              RFC 2672, August 1999.

   [RFC3597]  Gustafsson, A., "Handling of Unknown DNS Resource Record
              (RR) Types", RFC 3597, September 2003.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, March 2005.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.

   [RFC4592]  Lewis, E., "The Role of Wildcards in the Domain Name
              System", RFC 4592, July 2006.

9.2.  Informative References

   [RFC1912]  Barr, D., "Common DNS Operational and Configuration
              Errors", RFC 1912, February 1996.

   [RFC3363]  Bush, R., Durand, A., Fink, B., Gudmundsson, O., and T.
              Hain, "Representing Internet Protocol version 6 (IPv6)
              Addresses in the Domain Name System (DNS)", RFC 3363,
              August 2002.

   [RFC4294]  Loughney, J., "IPv6 Node Requirements", RFC 4294,
              April 2006.

Authors' Addresses

   Scott Rose
   NIST
   100 Bureau Dr.
   Gaithersburg, MD  20899
   USA

   Phone: +1-301-975-8439
   Fax:   +1-301-975-6238
   EMail: scottr@nist.gov

   Wouter Wijngaards
   NLnet Labs
   Kruislaan 419
   Amsterdam  1098 VA
   The Netherlands

   Phone: +31-20-888-4551
   EMail: wouter@nlnetlabs.nl

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